I haven't had any issues finding/making parts of the outfit except one: That undershirt! Does anyone have an idea of where to find something like it?
Thank you so much for all your help here! Much appreciated!

-His shirt is linen, but another cotton-based fabric with a visible weave will work.
-His vest is heavy drapery satin that secures to the shirt with snaps.
-The pants are double layered with a cotton filler towards the bottom to create the "poof" look with simple, elastic-gathered, bands at bottom.